31.2 CASE STUDY

How could you determine whether this infection was caused by HSV-1 or HSV-2?

To differentiate between HSV-1 and HSV-2, several specific diagnostic methods can be employed:

  • Type-specific PCR: Polymerase Chain Reaction (PCR) can be used to amplify specific regions of the HSV genome. There are DNA sequences that are distinct between HSV-1 and HSV-2, allowing for differentiation. By using primers specific to either HSV-1 or HSV-2, a PCR test can determine which type of the virus is present in the sample.

  • Viral Culture and Typing: If the virus grows in culture, it can be typed using type-specific antibodies. In this method, after the virus has been cultured, it is subjected to a test where antibodies specific to either HSV-1 or HSV-2 are introduced. If the virus present in the culture binds to the HSV-1 specific antibody, then it is HSV-1 and vice versa.

  • Type-specific Serological Tests: These tests detect antibodies against HSV in the blood. Some modern serological tests can differentiate between HSV-1 and HSV-2 antibodies. However, they indicate past or current infection and might not pinpoint the specific type causing a current outbreak unless it's a primary infection.

  • Direct Immunofluorescence with Type-specific Antibodies: As mentioned, direct immunofluorescence can be used with antibodies that specifically recognize either HSV-1 or HSV-2. When applied to a sample from the lesion, the virus will bind with the respective type-specific antibody, helping in differentiation.


In clinical practice, the differentiation between HSV-1 and HSV-2 is essential mainly for genital lesions, as HSV-2 is more commonly associated with genital herpes, while HSV-1 is more commonly associated with oral herpes. However, with changing sexual practices, HSV-1 is also being increasingly identified as the cause of genital lesions. In the described case, considering the location of the lesions (around the mouth), HSV-1 would be the more likely cause, but laboratory tests are necessary to confirm the type.

Mind Map: How could you determine whether this infection was caused by HSV-1 or HSV-2?

Type-specific PCR

  • Amplify specific regions of the HSV genome

  • Use primers specific to either HSV-1 or HSV-2

  • Determine which type of the virus is present in the sample

Viral Culture and Typing

  • Grow the virus in culture

  • Introduce type-specific antibodies

  • Binding to HSV-1 or HSV-2 antibody determines the type

Type-specific Serological Tests

  • Detect antibodies against HSV in the blood

  • Differentiate between HSV-1 and HSV-2 antibodies

  • Indicate past or current infection, may not pinpoint the specific type causing a current outbreak

Direct Immunofluorescence with Type-specific Antibodies

  • Apply type-specific antibodies to a sample from the lesion

  • Virus binds with respective type-specific antibody

  • Helps in differentiation

Clinical Importance

  • Differentiation essential for genital lesions

  • HSV-2 more commonly associated with genital herpes

  • HSV-1 more commonly associated with oral herpes

  • HSV-1 increasingly identified as the cause of genital lesions

  • Location of lesions (around the mouth) suggests HSV-1, but lab tests necessary to confirm type.